The present invention relates to piezoelectric optical materials and more particularly to Langasite-type crystals and the method for manufacturing these crystals.
Recent development of digital communications devices and demands for them are remarkable. The system for the recent mobile communications, including portable telephones and personal handy phones, has been rapidly expanding. In such a digitalized communications field, an improvement of performance in filters and oscillators incorporated in communications devices is very important.
Piezoelectric crystals are excellent electronic components and their properties are preferably used in the filters and oscillators of the communications devices. For example, the quartz is used in SAW (i.e., surface acoustic wave) filters of the portable telephones, and LiTaO.sub.3 is used in TV or VTR (or VCR) filters.
The quartz is robust against temperature change, however its band width is narrow. On the contrary, the LiTaO.sub.3 is weak against temperature change but its band width is wide.
Therefore, the recent research and development is directed to new materials which possess the excellent properties of both the quartz and the LiTaO.sub.3. Namely, the newly developed materials will be small in the frequency change when the temperature changes, stable in the oscillation, wide in the band width, and small in the insertion loss.
Among the conventionally developed crystals, .alpha.-AlPO.sub.4 is not suitable for the industrialized manufacturing due to generation of twin crystals and Li.sub.2 B.sub.4 O.sub.7 is deliquescent and low in the growth speed.